It is common practice to decorate the surface of manufactured articles to create an aesthetically pleasing look for the product. This has traditionally been accomplished through the use of liquid paints, typically containing solvents that evaporate from the paint leaving behind the solids in the form of a uniform film that decorates the surface of the article.
Traditional vehicle assembly methods typically include a spray painting step to paint visible vehicle parts and provide a protective and aesthetic appealing outer surface. However, the process of spray painting is time-consuming and generally involves volatile organic solvents that present special handling and/or environmental issues.
The transportation industry has sought to reduce solvents in vehicle assembly plants through the development and use of decorative colored films, known in the art as “paint films”. The original idea behind paint film was to utilize a conventional paint, which would simply be coated onto a liner and dried. The liner would then be releasably removed from the paint film which would then be applied to, for example, a three-dimensionally shaped vehicle body part. However, achieving a high quality application (for example, free of wrinkles and/or puckers) remains a serious concern with paint films, especially if applied to large or severely contoured surfaces.
There are two predominant techniques used to manufacture paint films: (1) solution-casting; and (2) extrusion. Each of these processes typically requires the use of elevated temperature (120° C. to 250° C. or more) to either evaporate the solvent (solution casting) or to melt the polymer (extrusion). Such temperatures are prone to thermally inducing shifts in color and other appearance properties of paint films, making color and appearance matching difficult to achieve.
High gloss and high image clarity are among the most common requirements for automotive finishes. While solvent based paints are typically capable of acceptable appearance, colored extruded plastic films fall well short of achieving a desirable rich “wet-look”. In order to improve the appearance of paints, a transparent clear coat (commonly known as a clear coat) is known to be applied onto the colored paint (commonly known as a base coat). Similarly, paint films may have a transparent clear layer supported on a colored base layer.
If paint films are applied to three-dimensional shaped vehicle parts problems may be encountered such as, for example, stretching, wrinkling, and/or puckering of the paint film during application that renders the finished body parts aesthetically, and possibly functionally, unsuitable. These problems may be made even worse by molecular orientation of the paint film (for example, during extrusion) such that stretchability of the paint film varies with film orientation.